UNDERSTANDING THE DIFFERENCES BETWEEN RGB, CMYK, CMYKOGV, AND SPOT COLORS
Often Pantone gets requests for more information about different color spaces and how, when, and why to use them. Before we begin exploring some of the available options, let’s quickly establish what a color space is. In the simplest of terms, a color space represents the specific organization of available colors within a given system or color model used to render a digital image. Different digital products and applications use different types of standardized color spaces, and some color spaces have a wider range of colors than others. We know not all designers are formally trained in the differences between color spaces, and even fewer have the time to dig around for answers on their own. But this information can make all the difference for brand owners and designers who want to know how to maintain the bold, vibrant, and realistic colors they specify in their projects, or better understand what to expect when these colors are printed or displayed on screen. So let’s review a breakdown of the different types of color provided in our Pantone Guides, on our site, and also in your design software.
The RGB system, used for digital display, is so named because it uses red, green, and blue as additive primaries to make a range of other colors. This means that, theoretically, the appearance of any color can be simulated by starting with black (no light) and adding certain proportions of red, green, and blue light. When the amounts of red, green, and blue are equal and at maximum intensity, we get white. One benefit of the RGB color space is that it presents a nice model for designing mass-producible devices that either imitate the eye (such as scanners and digital cameras), or attempt to fool the eye into believing it’s seeing many colors (as with digital screens and televisions). For example, a digital camera imitates color vision by measuring the intensities of red, green, and blue light reflected from the objects being photographed, whereas a computer monitor simulates colors by displaying different intensities of red, green, and blue light.
THE DIFFERENCE BETWEEN RGB AND sRGB
We’ve established that the RGB system offers a “recipe” used to create colors on digital displays using an additive color space. However, since every device is slightly different, the RGB values needed to reproduce any given color will vary from one device to another. In response to that variability, sRGB was created in 1996 as a system to define the color profile for a specific condition or device.
The sRGB profile was based upon the “typical” CRT monitor of that time, as perceived in an environment designed to match typical home and office viewing conditions. sRGB is the standard color space for computer monitors and the internet, since images and graphics will be viewed on many different device types in all sorts of uncontrolled conditions. Images from many consumer-grade digital devices, such as your phone or digital camera, may not have a color profile associated with them, so many workflows will assign a sRGB profile to the data as a “safe” option when the true color data is unknown.
However, because the sRGB color space is very small, graphics converted to sRGB from another color space will lose much of the color data.
If RGB is the simplest model of color reproduction on digital screens, CMY is its alter ego in print applications. Instead of starting with black and adding primary-colored lights to create a whole color gamut, as RGB does, the CMY model asks the fundamental question that defines color printing: “If we start with white, how would we to get back to black?” The answer the CMY color space offers is that we need to remove different quantities of red, green, and blue from our original white. In the case of color printing, we subtract red wavelengths of light from the white of a piece of paper by using a filtering pigment (ink), that allows all colors to pass through it except for red. What does “redless” ink look like? It’s the color we call cyan. Similarly, magenta could be considered “greenless” ink, and yellow can be considered “blueless” ink. The cyan, magenta, and yellow inks of CMY are called subtractive primaries because we start with white and use them to remove wavelengths of reflected light.
CMY works quite well in theory, but in practice, this method needs a little help. Due to the practical limitations of ink manufacturing and the realities of print technology, in order to get true black, we must use black ink in addition to the CMY primaries.
CMY AND THE PRACTICALITIES OF PRINTING: WHY DO WE NEED K?
The most common form of full-color printing is based on the clever use of red, green, and blue filters (in the form of cyan, magenta, and yellow ink, respectively) to subtract, or filter, different wavelengths from the white light reflected by the substrate. We can vary the amount of light filtered by each ink by allowing some of the background (substrate) to show through unfiltered. This is called ‘screening.’ A screened area with a uniform percentage of ink (for example a patch screened so that it is 70% cyan ink and 30% paper) is called a tint. Theoretically, when you combine equal tints of cyan, magenta, and yellow, you should get a neutral shade of gray,* and when all are at 100% ink and 0% paper, you should see black. However, commercial inks and papers are far from perfect, and when inks are printed on top of one other, they don’t always behave in an ideal way. It is practically impossible, for example, to manufacture a cyan ink that filters out only red and absolutely no green or blue. The result is that when you print a patch that is 100% cyan, magenta, and yellow, you don’t get a pure black. Instead, you get a muddy, dark brown patch of oversaturated ink that can cause drying issues and printed sheets that stick together. To get better blacks and grays (including the black ink needed for text), printers reduce the overall amounts of the CMY primaries and add quantities of black ink. “CMYB” would be a confusing name for this process as the letter B is frequently used to denote “blue.” So printers use the letter K, for “key,” to give us “CMYK,” also commonly referred to as four-color printing.
Printers like the fact that CMYK uses less ink, saves money, and shortens drying time. But CMYK is just one form of process color printing, a general term for any mechanism that generates colors using quantities of primary inks. In fact, there are some process-color systems that use up to seven or more primary inks.
It is useful to think of RGB and CMY as simple transformations of each other. In fact, CMY can be thought of as a special form of RGB—one that uses negative quantities of red, green, and blue. The key idea to remember with these two color spaces is that three primary colors, combined in different ways, are all that’s needed to fool the human eye into thinking it’s seeing all possible colors.
* In a perfect world, equal percentage tints of cyan, magenta, and yellow would produce a neutral gray. In reality, this is not the case because inks, substrates, and printing processes are far from ideal. Therefore, a neutral gray is never achieved by printing equal values of yellow, magenta, and cyan.
RGB and CMYK are what we refer to as device dependent color spaces, because the end results are so closely tied to the equipment and how it’s used. Just as no two monitors will display the same RGB values in exactly the same way, no two printing presses will reproduce a set of CMYK values exactly. In fact, due to the vast number of variables in the printing process, reproducing a given CMYK combination on six different presses will result in six different colors. The absorbency of the substrate, the growth in the size of the dots as they bleed, how well the layers of ink adhere to one another, and the ability of the individual inks to filter the light as desired are just some of the factors that combine to create a unique signature for every printing process and press. Add to this different levels of maintenance, as well as influences from one operator to another, and the nuanced variations in color become virtually limitless.
For this reason, neither RGB, nor CMYK values may be used to define a color. Rather, we need to think of RGB and CMYK as recipes used to create color. The particular recipe needed to reproduce a given color will vary from one device or process to another.
The biggest benefit of process printing formats like CMYK is that inks stay in the press and don’t need to be changed between jobs. However, while process is the most economical printing method, some colors are just too difficult to reproduce using only four colors. In a typical print environment, you can achieve about 55% of the Pantone Matching System® (PMS) Spot Colors (with a barely noticeable visual difference) using only CMYK.
Adding a fifth, sixth, or even seventh color to CMYK process printing can extend the gamut to increase the percentage of achievable Pantone Colors up to ~90%. Pantone has adopted our own formulation for Extended Color Gamut (ECG) printing by adding three more base inks, orange, green, and violet, to the CMYK ink set (creating CMYKOGV) in order to produce most of the total Pantone Spot Colors using process printing. The Extended Gamut format offers the same benefits of four-color process printing, with fewer limits to the number of PMS-matched colors that you can put into a job.
The demand for better, faster, and more economical color achievability is stronger than ever, and printing technology has improved to meet customers’ expectations for quality and efficiency. Extended Gamut print systems have also evolved, with 6-, 7-, and 8-color printing devices gaining popularity, especially for large format and digital printing. Globally, industry experts, leaders, and universities continue to push the possibilities through constant testing and technical advancements. For more information about Extended Gamut Printing, listen to The Gamut Podcast.
SPOT COLOR PRINTING
Printed colors created without screens or dots, such as those found in the Pantone Matching System (PMS), are called spot, or solid colors. Spot colors are specifically mixed from a range of solid inks, which tends to make them cleaner and brighter than colors created using a four-color process. Their purity and consistency make them well-suited for applications like corporate logos and identity programs, where even slight variations in color must be avoided. Using Pantone Spot Colors not only provides more saturated, vibrant color over process versions, but they also increase your ability to reproduce and communicate your color globally because Pantone Standards are referenced around the world. Because each color is individually mixed and loaded into the printer, spot color printing is best used for one-, two-, or three-color jobs, and can be more expensive to run than process printing.
Printers order specific spot colors by their identification number, or mix them using the Pantone Ink Mixing Formula. Creating a Pantone Spot Color is similar in concept to mixing yellow and blue paints to make green—only with a much greater degree of precision. Spot colors are mixed in the ink room or by an ink supplier, using a palette of 18 base ink colors and a unique Pantone Ink Mixing Formula. A Pantone Chip should be included with the ink as a reference, to help ensure the printer achieves the intended color intent on press. Spot colors are added to a single deck on the press and printed as a custom color, and when the job is done, the spot color ink must be removed.
To manufacture the 18 base inks used for mixing PMS Colors, ink manufacturers must be licensed by Pantone, and in order to retain their license, they must annually submit samples of the base ink colors for approval. These quality control measures help ensure Pantone Spot Colors are reproduced consistently around the world.
Before choosing a Pantone Spot Color for a job, it’s wise to evaluate how it will look in case it needs to be printed in four- or seven-color process, and not as a spot. Here are the Pantone References that can help you make the best decision for each job.